Mild bromination of unreactive aromatic compounds

Article abstract of DOI:10.1016/j.tetlet.2012.02.101

N,N,N', N'-Tetrabromobenzene-1,3-disulfonamide and poly(N, N'-dibromo-N-ethylene-benzene-1,3-disulfonamide) in concentrated H ₂SO₄ can be used as efficient reagents for the mild bromination of unreactive arenes at room temperature, under solvent-free conditions, in good yields.

Full text of DOI:10.1016/j.tetlet.2012.02.101

Tetrahedron Letters 53 (2012) 2325–2327
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Mild bromination of unreactive aromatic compounds
Ramin Ghorbani-Vaghei , Hajar Shahbazi , Hojat Veisi b
a,
⇑
a
a
Department of Organic Chemistry, Faculty of Chemistry, Bu-Ali Sina University, 65174 Hamedan, Iran
Department of Chemistry, Payame Noor University, 19395-4697 Tehran, Iran
b
a r t i c l e i n f o
a b s t r a c t
0
0
0
Article history:
N,N,N ,N -Tetrabromobenzene-1,3-disulfonamide and poly(N,N -dibromo-N-ethylene-benzene-1,3-
disulfonamide) in concentrated H SO can be used as efficient reagents for the mild bromination of unre-
active arenes at room temperature, under solvent-free conditions, in yields.
Received 8 January 2012
Revised 2 February 2012
Accepted 23 February 2012
Available online 3 March 2012
2
4
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Unreactive aromatic compounds
Electrophilic bromination
Solvent-free
TBBDA
PBBS
Halogenated aromatic compounds are a useful class of interme-
diates as they are precursors to a number of organometallic species
for the synthesis of natural products and pharmaceutically impor-
This reaction does not proceed in the absence of sulfuric acid,
and therefore the following mechanism is suggested (Scheme 2).
Acid catalysis plays an important role in the reaction of TBBDA with
deactivated arenes via O-protonation generating a cation, a reso-
nance contributor which makes it clear that this is an agent which
can act as an efficient bromonium-transfer agent. This superelectr-
ophilic agent is able to attack even relatively unreactive arenes.
The results of the bromination of some deactivated arenes are
presented in Table 1. 1,3-Dinitrobenzene, nitrobenzene, and penta-
fluorobenzeneweresuccessfullybrominatedundertheseconditions
(Table 1, entries 1–4). Our attempts to brominate benzonitrile over 4
hours failed.
1
tant compounds. There are many known methods for the prepara-
tion of haloarenes from aromatic compounds, especially from
electron-rich systems.2 However, few methods are known for the
halogenations of deactivated aromatics as harsh experimental con-
ditions are required for their preparation.3
N-Halo compounds have been studied extensively as electro-
philic halogenating agents for the halogenation of activated aro-
matic rings. The low reactivity of N-halo compounds with
deactivated arenes requires the addition of activating agents and
direct bromination methods have been recently developed using
2
r
the following bromonium donating reagents: TBCA/H
2
SO
4
,
NXS/
3
d
3e
BF
3
-H
2
O
and NBS/H
2
SO
4
.
EWG
0
0
EWG
N,N,N ,N -Tetrabromobenzene-1,3-disulfonamide [TBBDA] and
poly(N,N -dibromo-N-ethylene-benzene-1,3-disulfonamide) [PBBS]
are halogenating agents, and are effective catalysts for various or-
0
TBBDA or PBBS
2s
ganic transformations.4
98%H SO , r.t.
2 4
Br
0
0
In continuation of our interest in the application of N,N,N ,N -
tetrabromobenzene-1,3-disulfonamide [TBBDA] and poly(N,N -di-
0
EWG= Electron-withdrawing group
Br
bromo-N-ethylene-benzene-1,3-disulfonamide) [PBBS], in organic
4
synthesis, herein we report a simple and improved protocol for
the preparation of haloarene from unreactive aromatic com-
pounds. The reactions proceed in the presence of TBBDA and PBBS
Br
N
Br
N
Br
N
Br
Br
( N
S
S
S
S
2
CH CH2 )n
in strong acid (98% H
2 4
SO ), at room temperature, under solvent-
O
O
O
O
O
O
O
O
free conditions (Scheme 1).
TBBDA
Scheme 1. Bromination of unreactive aromatic compounds.
PBBS
⇑
Corresponding author. Tel./fax: +98 811 8380709.
E-mail address: rgvaghei@yahoo.com (R. Ghorbani-Vaghei).
0
040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2012.02.101

2
326
R. Ghorbani-Vaghei et al. / Tetrahedron Letters 53 (2012) 2325–2327
Br
N
Br
Br
Br
N
Br
Br
H SO
2
4
N
+
Br
S
O O
S
O O
N
Br
S
S
O
O
O
OH
TBBDA
EWG
EWG
4
Br
N
Br
H SO
NH2
2
4
+
H N
2
+ 4
S
S
Br
Br
HSO4
N
Br
O O
O
O
S
O
S
O
O
OH
Scheme 2. Suggested mechanism for bromination of unreactive aromatic compounds.
Table 1
Bromination of various unreactive arenes using TBBDA or PBBS at room temperature
Entry
Substrate
Producta
TBBDA
PBBS
Ref.
2r
Time (h)
4
Yield (%)
88
Time (h)
8
Yield (%)
71
NO2
NO2
1
NO2
Br
NO2
NO2
NO2
NO2
2
3
4
6
63
73
8
55
64
2r
5
Br
NO2
10
Br
F
Br
F
F
F
F
Br
F
4
5
1
4
76
—
2
4
70
—
2r
—
F
F
F
F
CN
No reaction
a
Products were characterized from their physical properties, by comparison with authentic samples, and by spectroscopic methods.
0
0
N,N,N ,N -Tetrabromobenzene-1,3-disulfonamide [TBBDA] and
10:2). The mixture was poured onto crushed ice (30 g), neutralized
with 5% NaOH and extracted with cold CH Cl
ganic layer, was dried, evaporated, and the product was collected
and recrystallized from hexane [yellow solid, 88% (using TBBDA),
mp 74–76 °C ]. IR (KBr): 3098, 2925, 1808, 1747, 1616, 1595,
0
poly(N,N -dibromo-N-ethylene-benzene-1,3-disulfonamide) [PBBS]
are stable, non-volatile, inexpensive, and safe reagents.
2
2
(2 ꢀ 30 mL). The or-
In conclusion, we have described the application of TBBDA and
PBBS in 98% H SO for the bromination of deactivated aromatic
2 4
compounds under solvent-free conditions.
1534, 1344, 1309, 1162, 1075, 915, 897, 741, 726, 638, 517, 488;
1
H NMR [DMSO-d
6
, 500 MHz]: d
C NMR [DMSO-d , 125 MHz]: d
49.5; MS [m/z] 246 [M ], 248 [M+2] .
H
(ppm) 8.80 (1H, s), 8.83 (2H, s),
1
3
6
C
(ppm) 118.7, 123.7, 132.9,
Typical procedure for the preparation of 1-bromo-3,5-
dinitrobenzene
+
+
1
9
8% H
2 mmol) and TBBDA (0.25 g, 0.45 mmol) or PBBS (0.45 g) in a
5 mL flask. The flask was closed, and the mixture was stirred at
2
SO
4
(4 mL) was added to a mixture of 1,3-dinitrobenzene
Acknowledgment
(
2
We are thankful to Bu-Ali Sina University, Center of Excellence
and Development of Chemical Methods (CEDCM) for financial
support.
room temperature for the specified period of time (Table 1). The
progress of the reaction was monitored by TLC (n-hexane/acetone,

R. Ghorbani-Vaghei et al. / Tetrahedron Letters 53 (2012) 2325–2327
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